Corrosion inhibitors and methods of using same



United States Patent Ofifice 3,335,096 CORROSION INIHBITORS AND METHODS OF USING SAME George B. Hatch, Allison Park, Pa., assignor to Calgon Corporation No Drawing. Filed July 16, 1964, Ser. No. 383,222 12 Claims. (Cl. 252-389) This invention relates to new corrosion inhibiting compositions consisting essentially of sodium nitrite, sodium tetraborate, benzotriazole, and sodium silicofluoride, and mixtures thereof with sodium bicarbonate or carbonate, and to the method of inhibiting metal corrosion in closed water systems therewith.

High maintenance and replacement costs due to corrosion, deposition, valve and pump difficulties, untimely plugging of heat exchangers as well as equipment failures, have long been serious problems in closed circulating water systems, especially in view of the increasing use and complexity of closed system machinery such as diesels, internal combustion engines and high temperature hot water systems.

Sodium nitrite-sodium tetraborate-benzotriazole compositions have been used as corrosion inhibitors in essentially closed water systems for a number of years. See

Liddell Patent No. 2,877,188. These compositions have given good protection for ferrous metals, copper and copper alloys, but they actually accelerate the corrosion of aluminum, lead and alloys of lead such as soft solder, i.e., lead-tin solder.

Although I am uncertain of the mechanism, I have found that the addition of sodium silicofluoride or mixtures of sodium silicofluoride and sodium bicarbonate or carbonate to a basic sodium nitrite-sodium tetraboratebenzotriazole composition substantially reduces the corrosion of aluminum, lead, and soft solder 'without impairing the effective corrosion inhibition of the other common metals used in closed water systems.

My invention includes compositions containing about 2390% sodium nitrite, about 9.975% sodium tetraborate (calculated as the pentahydrate), about 0.1% ben- 3,335,096 Patented Aug. 8, 1967 The preferred composition of my invention contains about 50-76% sodium nitrite, about -40% sodium tetraborate (calculated as the pentahydrate), 0.5-3%

15 benzotriazole, sodium silicofluoride in about 34% of the amount of sodium tetraborate, and sodium bicarbonate in up to about 5% of the amount of sodium nitrite.

The following experiments with examples of the compositions of my invention demonstrate their effective- 20 ness as metal corrosion inhibitors.

Weighed metal specimens we're immersed in solutions of various corrosion inhibiting compositions dissolved in water containing 19 p.p.m. calcium, 6.0 ppm. magnesium (total hardness thus calculated at 77 ppm. CaCO 18 p.p.m. chloride, and 12 ppm. bicarbonate and agitated therein for five days at 35 C. After this five day exposure the metals were removed and cleaned with pickle solutions consisting of 10% H 50 f-or admiralty, copper, and tin, 5% of 37% HCl for aluminum, 18.5% HCl and 0.1% dibutylthiourea for steel, 25% ammonium acetate for lead and soft solder, and reweighed. In order to correct for weight loss due to pickling, identical metal specimens which were not subjected to corrosion were weighed, pickled, and reweighed, and the weight loss of these blanks was subtracted from the weight loss of their respective corrosion test specimens. Using this figure as the weight loss due to corrosion, the loss of metal in milligrams per square decimeter per day was calculated.

Table I lists the concentrations and ingredients of various corrosion inhibiting compositions used in these experiments.

TABLE I NaNO percent Benzotriazole, Na B4O1.5H 0,

percent NaH 0 03,

percent IIQBOB, percent Table II demonstrates the effectiveness of various examples of my invention in inhibiting corrosion under the conditions specified. It will be seen that my improved compositions (V-X) have substantially reduced the corrosion of aluminum, soft solder, and lead, without af- 4. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 2 in amounts sufficient to maintain the concentration of sodium nitrite at between about 500 and about 5 fectmg the corrosion inhibitlon of the other metals. 20,000 p.p.m.

TABLE II Solder Composi- Steel Admiralty 2 Aluminum Lead Tin Copper tion A B G Control 166 3. 9 I 0.2 0.1

"""""" "6.6 "fib Zii 0.1 0.3 0.1 0.1 0.1

AISI-SAE 1010. 1 ASIM B171.

Solder A is 50% lead, 50% tin; Solder B is 60% lead, 40% tin; Solder C is 70% lead, 30% tin; all figures given as metal loss in milligrams per square decimeter per day, many being averages of numerous tests. The control was carried out under identical conditions, but no corrosion inhibitor was added.

The compositions of my invention may be added to closed water systems in sufiicient amounts to maintain the concentration of sodium nitrite at from about 500 to about 20,000 p.p.m., but it is most economical to maintain the sodium nitrite concentration at 1000-3000 p.p.m.

The pH range in the water system may be maintained from about 7 to about 9, but it is preferable to have a pH of about 8-8.5 and to obtain this pH by regulating the relative amounts of sodium tetraborate and sodium silicofluoride.

Thus, my invention relates to improved corrosion inhibiting compositions consisting essentially of sodium nitrite, sodium tetraborate, benzotriazole, sodium silicofiuoride, and mixtures thereof with sodium bicarbonate or carbonate, and to the method of inhibiting the corrosion of metals in closed water systems therewith.

I do not intend to be limited to the specific compositions disclosed herein for illustrative purposes. My invention may be otherwise practiced and embodied within the scope of the following claims.

I claim:

1. A composition for inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems consisting essentially of about 23-90% sodium nitrite, about 99-75% sodium tetraborate (calculated as the pentahydrate), about 0.1-% benzotriazole, sodium silicofiuoride at about 20-34% of the amount of sodium tetraborate, and a sodium salt of carbonic acid in a quantity sufficient to supply bicarbonate ions in up to about 5% of the amount of sodium nitrite.

2. A composition for inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems consisting essentially of about 5076% sodium nitrite, about -40% sodium tetraborate (calculated as the pentahydrate), about 0.5-3% benzotriazole, sodium silicofiuoride at about 34% of the amount of sodium tetraborate, and a sodium salt of carbonic acid in a quantity sufficient to supply bicarbonate ions in up to about 5% of the amount of sodium nitrite.

3. A method of inhibiting corrosion of ferrous metals, copper, aluminium, lead or tin in closed water systems comprising adding to said systems the composition of claim 1 in amounts suflicient to maintain the concentration of sodium nitrite at between about 500 and about 20,000 p.p.m.

5. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 1 in amounts sufficient to maintain the concentration of sodium nitrite at between about 500 and about 20,000 p.p.m., the amount of sodium tetraborate and sodium silicofiuoride in said composition being such as to obtain a pH in the system of between about 8.0 and about 8.5.

6. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 2 in amounts sufficient to maintain the concentration of sodium nitrite at between about 500 and about 20,000 p.p.m., the amount of sodium tetraborate and sodium silicofiuoride in said composition being such as to obtain a pH in the system of between about 8.0 and 8.5.

7. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 1 in amounts sufiicient to maintain the concentration of sodium nitrite at between about 1,000 and about 3,000 p.p.m.

8. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 2 in amounts sufficient to maintain the concentration of sodium nitrite at between about 1,000 and about 3,000 p.p.m.

9. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 1 in amounts sufficient to maintain the concentration of sodium nitrite at between about 1,000 and about 3,000 p.p.m., the amount of sodium tetraborate and sodium silicofiuoride in said composition being such as to obtain a pH in the system of between about 8.0 and about 8.5.

10. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 2 in amounts sufiicient to maintain the concentration of sodium nitrite at between about 1,000 and about 3,000 p.p.m., the amount of sodium tetraborate and sodium silicofiuoride in said composition being such as to obtain a pH in the system of between about 8.0 and 8.5.

11. A method of inhibiting corrosion of ferrous metals, copper, aluminum, lead or tin in closed water systems comprising adding to said systems the composition of claim 1 in amounts suflicient to maintain the concentration of sodium nitrite at between about 500 and about 20,000 p.p.m., and maintaining a pH in said systems of between about 7 and about 9.

12. A method of inhibiting corrosion of ferrous metals,

copper, aluminum, lead or tin in closed water systems 5 References Cited UNITED STATES PATENTS 2,795,560 6/1957 Williams 252-387 2,877,188 3/1959 Liddell 252--389 3,024,099 3/ 1962 Martinson 252-387 LEON D. ROSDOL, Primary Examiner. SAMUEL H. BLECH, Examiner.

10 M. WEINBLATT, Assistant Examiner. 

1. A COMPOSITION FOR INHIBITING CORROSION OF FERROUS METALS, COPPER ALUMINUM, LEAD OR TIN IN CLOSED WATER SYSTEMS CONSISTING ESSENTIALLY OF ABOUT 23-90% SODIUM NITRITE, ABOUT 9.9-75% SODIUM TETRABORATE (CALCULATED AS THE PENTAHYDRATE), ABOUT 0.1-5% BENZOTRIAZOLE, SODIUM SILICOFLUORIDE AT ABOUT 20I34% OF THE AMOUNT OF SODIUM TETRABORATE, AND A SODIUM SALT OF CARBONIC ACID IN A QUANTITY SUFFICIENT TO SUPPLY BICARBONATE IONS IN UP TO ABOUT 50% OF THE AMOUNT OF SODIUM NITRITE. 